using PdfSharp;
using PdfSharp.Pdf;
using PdfSharp.Pdf.IO;
using PdfSharp.Drawing;

  private void esportaimmagine()
        {
            const string filename = @"C:\log\miofile.pdf";

            PdfDocument document = PdfReader.Open(filename);

            int imageCount = 0;

            foreach (PdfPage page in document.Pages)
            {

                PdfDictionary resources = page.Elements.GetDictionary("/Resources");
                if (resources != null)
                {

                    PdfDictionary xObjects = resources.Elements.GetDictionary("/XObject");
                    
                    if (xObjects != null)
                    {
                        ICollection<PdfItem> items = xObjects.Elements.Values;

                        foreach (PdfItem item in items)
                        {

                            PdfSharp.Pdf.Advanced.PdfReference reference = (PdfSharp.Pdf.Advanced.PdfReference)item;
                            
                            if (reference != null)
                            {
                                PdfDictionary xObject = reference.Value as PdfDictionary;

                                if (xObject != null && xObject.Elements.GetString("/Subtype") == "/Image")
                                {
                                    ExportJpegImage(xObject, ref imageCount);
                                }
                            }
                        }
                    }
                }
            }
            System.Windows.Forms. MessageBox.Show(imageCount + " images exported.", "Export Images");
        }

        void ExportJpegImage(PdfDictionary image, ref int count)
        {
            
            byte[] stream = image.Stream.Value;            
            FileStream fs = new FileStream(String.Format(@"c:\log\Image{0}.jpeg", count++), FileMode.Create, FileAccess.Write);
            BinaryWriter bw = new BinaryWriter(fs);
            bw.Write(stream);
            bw.Close();
        }